This invention relates to flexure joints in general. More particularly, this invention relates to a flexure which provides a joint between two objects, the flexure being very stiff against translational forces along its long axis, but permitting small angle rotation around the two axes normal to the long axis as well as around the long axis. Thus, the invention may be said to provide the action of a limited range ball joint without lost motion as it is operable with three degrees of freedom over small angles.
Various types of flexure joints have been developed to permit small amounts of rotation of one joined object relative to the other. Generally, however, the flexure joints of the art do not permit rotation around three axes. Thus, for example, U.S. Pat. No. 4,128,352, to Newell, and U.S. Pat. No. 3,844,663 to Raines both provide a two axis flexure, while U.S. Pat. No. 3,844,663 to Prette permits one degree of freedom. Other flexures available in the art often fail to exhibit the required degree of stiffness with respect to translational forces, and many suffer from the problems of stick slip or lost motion. The latter problems are especially evident in ball joints which are designed to provide rotation around all three axes. Thus, if the socket is tight around the ball, the ball sticks in the socket until enough force is provided to overcome the friction. This causes the force/displacement relationship to be unpredictable thereby making precise control difficult. On the other hand, if the ball is loose in the socket, the positioning of the ball cannot be completely controlled to the microinch level of precision (due to inherent uncertainty) as is often required in interferometry or microlithography. Ball joints, as well as other joints provided in the art also suffer from the requirement that they be lubricated, which in certain circumstances, such as space applications, leads to undesirable outgassing and depletion problems as well as temperature limitations.